The invention relates to a process for regenerating a catalyst, in particular a plate-type or honeycomb catalyst, which has been at least partially deactivated by catalyst poisons, the catalyst being treated with a gaseous reducing agent in order to remove the catalyst poisons.
Catalysts, such as for example plate-type and honeycomb catalysts, which are preferably configured as oxidation or reduction catalysts, are used in particular to clean off-gases or exhaust gases. These gas cleaning catalysts are poisoned and deactivated during use by catalyst poisons which are contained in the gases, in the form, for example, of heavy metals, such as mercury, arsenic, thallium, etc. This xe2x80x9cpoisoningxe2x80x9d of the catalysts results from the deposition of heavy metal compounds (oxides, sulfates) and arsenic oxides and from arsenic compounds and/or phosphates of these active components formed as a result of a reaction with catalyst active components, such as for example W, V, Mo, Fe, Cu, Co, Ni, Cr.
On account of the high costs involved in replacing a deactivated catalyst with a new catalyst, regeneration processes involving washing the catalysts have been developed. Japanese Patent JP 07222924 C in the name of MITSUBISHI has disclosed a regeneration process of this type for a deNOx catalyst in which the catalyst can be reactivated by washing with water or dilute inorganic acid followed by washing with oxalic acid and finally washing with water.
Japanese Patent JP 52063891 C discloses a regeneration process for a deactivated TiO2/V2O5 catalyst in which the washing is carried out using a 5% strength NH3 solution. A process in which the catalyst is washed with an oxalic acid and is then impregnated with a vanadium compound is known from Japanese Patent JP 54010294 C.
Published, European Patent Application EP 0 824 039 A1, Published, Non-Prosecuted German Patent Application DE 34 30 887 A1, German Patent DE 1 171 206 B and Chem. Abstr. No. 91:26538 relating to Japanese Patent Application JP 7902986 A disclose processes for regenerating a catalyst in which the catalyst is treated with a gaseous reducing agent.
In the process which is known from Published, European Patent Application EP 0 824 039 A1, a catalyst which has been poisoned by arsenic is treated with a gaseous reducing agent, such as H2, CO and CH4, during a thermal treatment.
In Published, Non-Prosecuted German Patent Application DE 34 30 887 A1, a process is described for reactivating a catalyst which has been used to remove NOx from flue gases, the catalyst is exposed to a heated stream of carbon monoxide in a reducing atmosphere.
The process described in German Patent DE 1 171 206 B relates to the regeneration of lead-contaminated catalysts for cleaning exhaust gases from internal combustion engines. In this case, the contaminated catalyst is regenerated with a reducing gas, such as hydrogen, carbon monoxide and hydrocarbons, at elevated temperatures.
The publication Chem. Abstr. No. 91:26538 relating to Japanese Patent Application JP 7902986 A deals with the regeneration of desulfurization and denitrification catalysts. In this case, the catalyst is regenerated in a reducing gas at between 700 and 1000xc2x0 C.
A drawback of the known processes for regenerating the catalysts by washing with water or acids and/or subsequently applying active components is that soluble or partially soluble catalyst active components are washed out, with the result that the efficiency of the catalytic converter is reduced.
It is accordingly an object of the invention to provide a process for regenerating a deactivated catalyst which overcomes the above-mentioned disadvantages of the prior art methods of this general type, in which the regeneration effect is improved.
With the foregoing and other objects in view there is provided, in accordance with the invention, a process for regenerating catalysts. The process includes treating a catalyst with a gaseous reducing agent to remove catalyst poisons; and washing the catalyst with a polyfunctional complex-forming agent. The polyfunctional complex-forming agent is a hydroxycarboxylic acid, a hydroxydicarboxylic acid solution or a solution of organic amines.
According to the first alternative, the object is achieved, according to the invention, by the fact that, following the treatment with the gaseous reducing agent, the catalyst is washed with a polyfunctional complex-forming agent, the polyfunctional complex-forming agent used being a hydroxycarboxylic acid, a hydroxydicarboxylic acid solution or a solution of organic amines.
In accordance with an added feature of the invention, there is the step of subjecting the catalyst to an impregnation process with at least one catalyst active component, which is suspended or dissolved in the polyfunctional complex-forming agent, after the washing step.
In accordance with an additional feature of the invention, there is the step of selecting the catalyst active component from W, V, Mo, Fe, Cu, Fe, Co, Ni, and/or Cr.
In accordance with another feature of the invention, the catalyst is a plate-type catalyst or a honeycomb catalyst which has been at least partially deactivated by the catalyst poisons.
In accordance with a further feature of the invention, after the washing step, there is the step of drying the catalyst at a temperature of below 70xc2x0 C. with air being passed through it.
In accordance with another added feature of the invention, there is the step of subjecting the catalyst to at least one thermal treatment process immediately after the catalyst has been treated with the gaseous reducing agent, after the catalyst has been washed with polyfunctional complex-forming agents, after the impregnation process with the polyfunctional complex-forming agent containing the catalyst active component, and/or after the drying of the catalyst step.
In accordance with another additional feature of the invention, there is the step of carrying out the thermal treatment process within a temperature range of from 100 to 500xc2x0 C.
With the foregoing and other objects in view there is further provided, in accordance with the invention, a process for regenerating catalysts. The process includes treating a catalyst with a gaseous reducing agent to remove catalyst poisons; and subjecting the catalyst to an impregnation process with at least one catalyst active component. The catalyst active component is suspended or dissolved in a polyfunctional complex-forming agent, and the polyfunctional complex-forming agent used is a hydroxycarboxylic acid, a hydroxydicarboxylic acid solution or a solution of organic amines.
According to the second alternative, the object is achieved, according to the invention, by the fact that, following the treatment with the gaseous reducing agent, the catalyst is subjected to an impregnation process with at least one catalyst active component which is suspended or dissolved in a polyfunctional complex-forming agent, the polyfunctional complex-forming agent used being a hydroxycarboxylic acid, a hydroxydicarboxylic acid solution or a solution of organic amines.
In accordance with a concomitant feature of the invention, there is the step of subjecting the catalyst to at least one thermal treatment process immediately after the catalyst has been treated with the gaseous reducing agent, after the impregnation process with the polyfunctional complex-forming agent containing the catalyst active component, and/or after the drying of the catalyst step.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is and described herein as a process for regenerating a deactivated catalyst, it is nevertheless not intended to be limited to the details described, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments.